The present invention relates to systems for pumping liquids under relatively high pressures. More particularly, the invention relates to a portable system for pumping liquids, wherein liquid pressure is regulated by a transducer which develops electrical control signals for controlling an electric motor drive source.
The present invention is primarily adaptable for use with portable high-pressure spraying systems for spraying coating materials such as paint and the like. However, the invention is also adaptable for use in connection with any high-pressure liquid spraying system, particularly of a portable nature wherein the driving force is an electrical motor or equivalent. Portable spraying systems of this general classification are known in the art, and are generally typified by an electrical motor drive source which is mechanically linked to drive a reciprocable pump, wherein the liquid pressure is controlled by a pressure transducer coupled to an electric motor switching circuit. The pressure transducer monitors the liquid output pressure from the pump, and controls a switching circuit which applies an electrical driving voltage to the motor when the monitored pressure drops below a predetermined or preset amount, and provides a motor shut-off control signal whenever the pressure exceeds a predetermined or preset higher value.
Portable pumping systems of the type generally related to the present invention are disclosed in U.S. Pat. No. 4,009,971, issued Mar. 1, 1977, and U.S. Pat. No. 4,397,610, issued Aug. 9, 1983. The '971 patent discloses a portable pumping system having a positive on/off motor control, wherein a pressure transducer is connected into a liquid manifold and may be preset to a predetermined pressure which causes the transducer to activate an electrical switch for controlling power delivered to the motor. The '610 patent discloses a variable speed motor utilizing a pressure transducer to generate a variable drive voltage to the motor, to slow down and speed up the drive motor in response to pressure fluctuations. Various forms of pressure transducer have been developed for use in connection with pumps of the general type associated with the present invention. For example, U.S. Pat. No. 4,212,591, issued Jul. 15, 1980, discloses a pressure transducer which senses the expansion and contraction of a flexible pressure hose as a means for determining liquid pressure. The U.S. Pat. No. 4,335,999, issued Jun. 22, 1982, discloses a further variation of the flexible hose sensing mechanism. U.S. Pat. No. 4,323,741, issued Apr. 6, 1982, discloses a Bourdon tube construction wherein the deflection of the Bourdon tube causes a switch activation to occur. The aforementioned '971 patent discloses a pressure transducer comprising a slidable piston rod responsive to pressure, the piston rod having a threadable knob at its distal end, the knob being engageable against a pin which is movable to contact a switch lever. Each of the foregoing patents disclose various forms of reciprocable drive liquid pumping cylinders having an output liquid delivery line coupled to a pressure sensor, via either a simple manifold or liquid flow-through device, and an output delivery line coupled to the pressure sensor mechanism.